Attention has been attracted to various functional substances contained in Japanese tea that has been drunk by Japanese for a long time due to current boom of health. A representative example thereof as catechins. Catechins were first confirmed by Dr. Tsujimura, et al. in 1929 at The Institute of Physical and Chemical Research. Then, various functions of catechins such as an antioxidation action, an antibiotic action, prevention of cancer, and decrease in blood cholesterol level have been found. Products such as foods for specified health uses and supplements have been made from catechins.
However, production of green tea that contains a large amount of catechins is restricted to some regions such as Japan and China, and fermented tea such as black tea and oolong tea is produced in about 80% of the world. In recent years, it has been clear that the fermented tea contains substances having the same function as that of catechins, which are called theaflavins, and attention has been attracted (Patent Literature 1). Further, a method for synthesizing theaflavins has been studied (Patent Literatures 2 and 3).